AC plasma display panels are presently in commercial use as digitally addressable information display devices. The panel itself consists of two glass plates with a gas mixture sealed between them. A plurality of X-axis electrodes extend in a mutually parallel array on an interior substrate of one plate, and a plurality of Y-axis electrodes extend in a mutually parallel array on the interior of the other plate. The X-axis electrodes are at a ninety degree angle to the Y-axis electrodes, thereby forming a plurality of intersections between the X-axis and Y-axis electrodes. The typical commercially available AC plasma panel has 512 X-axis electrodes and 512 Y-axis electrodes, yielding 262,144 intersections.
When a voltage of between 180 and 200 volts is applied across an X-axis electrode and a Y-axis electrode, a discharge in the gas at the intersection between the electrodes occurs, causing a pulse of light to be emitted at the intersection of these elements. Once such discharge has been produced, it may be continuously maintained by the impression of a lesser AC sustain voltage between the electrodes, which causes the gas to emit a pulse of light at each transition of the applied AC waveform. This sustain voltage, however, is insufficient to initiate a discharge at an X-Y intersection. This phenomenon is known as inherent memory, and was originally disclosed by Baker et al in U.S. Pat. No. 3,499,167, and by Bitzer et al in U.S. Pat. No. 3,959,190. By precisely timing, shaping, and phasing multiple alternating voltage waveforms supplied to X and Y axes electrodes, the generation, sustaining, and erasure of light emitting gas discharges at selected locations on the plasma display panel can be controlled.
Prior art devices have typically used multiple level alternating voltage sustainer drive signals which are applied to both the X and Y electrodes, and present a composite sustainer waveform across the gas at each cell or point in the display panel where the X and Y electrodes intersect. Each of the X and Y electrodes in the past devices has been driven by one of the two separate complex sustainer circuits, operating typically at 95 volts. An improvement to this system was disclosed in U.S. Pat. No. 4,180,762, issued Dec. 25, 1979, to Larry Francis Weber and assigned to Interstate Electronics Corporation. This patent disclosed a means by which a single sustainer circuit is connected to one axis only of the panel electrodes, and accomplishes the sustaining function for all of the intersections in the panel.
Past systems typically required at least seven voltage levels to be supplied from the power supply, some of these levels required to be floating. These numerous voltage levels were required in order for the circuitry to generate the particular waveform required to control the generation, sustaining, and erasure of light emitting gas discharges at the selected location in the plasma display panel. Since an AC plasma display unit is generally packaged in one unit with its power supply contained within the unit, the requirement of numerous voltage levels presents the specific disadvantages of: (a) the size of the power supply; (b) difficulties in cooling the power supply; and (c) power dissipation problems within the circuitry of the display itself associated with the numerous voltage levels required. A further disadvantage of the requirement of numerous voltage levels is that such systems are costly to produce and test, and must frequently have the voltage levels adjusted.
Previous sustainer designs have also required at least two logical inputs, one input controlling the high output level of the sustainer, and the second input controlling the low output level of the sustainer. If these inputs do not have the proper phase relationship to each other, serious damage could occcur to the sustainer circuit, generally resulting in the destruction of part or all of the sustainer circuitry.